People log out during combat?

So I have no idea what this is about.
(for fun, no killing) i used sap on some target.
When 10 s duration was like 0.5s and used second sap. There was a 4 s timer. And when there was 2s to left sap... guy just dissapeared (hunter, warrior no matter)

I used fan of knives 0.5s after that happen. Nothing. They just disappeared from the game.

Next time and used hunter trap. There was like 2-1 s duration left and again. Some guy disappeared from the game!

As if they logged out instantly from game (during combat???)

What is this about?

And it happened like outside of gadgetzan arround scorpions or or the middle of nowhere in desolace land